Ultrastable Silicon Cavity in a Continuously Operating Closed-Cycle Cryostat at 4 K

Area of Science:

• Physics
• Optical Engineering
• Metrology

Background:

• Optical clocks require highly stable lasers for precise timekeeping.
• Previous low-temperature laser systems faced limitations in instability and linewidth.
• Achieving lower thermal noise is crucial for reaching 10^{-18} instability goals.

Purpose of the Study:

• To demonstrate a laser system with significantly improved instability and linewidth.
• To explore the benefits of low-temperature operation for laser stability.
• To assess the technical readiness for next-generation ultrastable lasers.

Main Methods:

• A laser was locked to a silicon cavity.
• The system operated continuously at a cryogenic temperature of 4 Kelvin.
• Performance metrics including instability and linewidth were measured at 1542 nm.

Main Results:

• The laser achieved a short-term instability of 1x10^{-16}.
• A median linewidth of 17 mHz was recorded.
• This represents a tenfold improvement in short-term instability and a 10^4 improvement in linewidth compared to prior sub-10 K systems.

Conclusions:

• Continuous 4 K operation of a silicon-cavity laser significantly reduces thermal noise.
• The demonstrated performance indicates readiness for developing next-generation ultrastable lasers.
• This work is a key step towards achieving the 10^{-18} instability target for optical clocks.